In South Korea heightened tension with the North is dominating the country’s three-nation summit with Japan and China.

The Japanese prime minister Yukio Hatoyama paid tribute to the 46 South Korean sailors who died in last week’s sinking of a naval ship.

Seoul believes North Korea torpedoed the vessel and says an international investigation proves it.

Japan is to toughen sanctions against North Korea, and has joined forces with the South and the US in calling on China to take a stand on the sinking. But Beijing has not apportioned blame.

The Chinese Premier Wen Jiabao, beginning his three-day visit to South Korea, said he understood the country’s grief and condemned acts threatening stability on the peninsula.

He said China would not protect whoever sank the warship. But so far it has not accepted the findings of the investigation.

Seoul is seeking action against the North via the UN Security Council – and China’s backing will be crucial.